Nuclear phosphoprotein phosphatase is involved in the dephosphorylation of nuclear phosphoproteins and this process may have the importance of affecting gene activity. The following studies on this enzyme are proposed. 1. The different forms of the phosphatase will be isolated, and at least one of the major forms will be purified to homogenity or to the highest attainable specific activity. 2. The properties of the phosphatases will be studied. The subunit structure and the interconvertibility of the multiple forms will be examined with gel electrophoresis and colunm chromtography as well as by treatment with ethanol or urea. 3. The relationship among the multiple forms and between the nuclear and cytosol phosphatases will be studied by immunochemical techniques using antisera prepared against the purified phosphatase. 4. The substrate specificity will be studied using phosphohistones and different fractions of nuclear nonhistone phosphoproteins as substrates. Special effort will be put into the preparation and fractionation of P32-phosphorylated nonhistone proteins. 5. The effects of metal ions, nucleotides (including cAMP and cGMP), histones, and DNA on the phosphatase activity will be studied to shed light on the possible mechanisms which control th phosphatase activity. 6. The possible role of nuclear phosphoprotein phosphatase in affecting gene replication will be examined by studying a) the effect of this enzyme on the activity of a partially purified RNA polymerase preparation, b) the effects of this enzyme and the antisera against the enzyme on the RNA synthesis of a broken-nucleus replication system, and c) correlations between gene activity and phosphatase activity in regenerating livers, during phenobarbital induction and in two hepatoma systems.